Most prior art printers comprise a print controller for receiving print information from a computer. The print information is usually supplied in a page description language, such as Adobe PostScript. The print controller takes the print information and performs operations on it in order to convert t to a form suitable for supply to one or more printheads. These operations can include, for example, decompression of compressed data, rasterization, compositing and scaling. Most printers have a print controller that supplies processed data to a singe printhead.
In duplex printers, both sides of a page need to be printed. Often, this is achieved by printing one side of the page first, followed by the other side, sometimes using the same printhead. In other embodiment, a pair of printheads are used, one for printing either side of the page. In U.S. Pat. No. 5,784,077 (Silverbrook), a pair of printheads are disposed at different points along a paper pathway.
Prior art arrangement make registration between information printed on respective front and rear sides of a page relatively difficult to achieve.